Creating a Mailbox
When a mailbox is created to pass objects (not data) it is a high-performance queue with a maximum size of 64 objects: MAILBOX_DEPTH. This queue is a block of memory that stores objects waiting to be sent or received. It is permanently assigned to the mailbox, and the unused portion of the queue is unavailable for other uses.
To get the best tradeoff between memory and performance, choose a size for the high-performance queue that is large enough for normal operations, and let the overflow queue handle unusual circumstances.
The MAILBOX_DEPTH bits are ignored for a data mailbox.